To store large amounts of gas under high pressure is not an easy task. Storage vessels for large volumes and high pressure become heavy and difficult to handle. Depending on the application there is also a considerable safety margin that must be taken into account, adding to the overall system mass. Releasing of gas must be done to a suitable low working pressure, which includes failure safe pressure regulators. The filling of big high pressure vessels can also be a safety issue.
In particular, there is an interest in using hydrogen for reducing the use of fossil fuels. The energy density per unit weight is very high and production is easily performed e.g. by water electrolysis. Furthermore, the exhausts do not harm the environment being plain water. Attention has been drawn also to use hydrogen as fuel in micro-power plants, e.g. in vehicles or even in personal electronics instead of battery operation. However, major drawbacks to the general use of hydrogen are connected to the high volatile properties and that it is difficult to store and distribute.
The pressure resistance of a spherical gas storage tank depends mainly on three factors. These factors are the size, the tank material, and the wall thickness. When all factors are considered, small containers represent, at least theoretically, a good solution with regard to the relation between the amount of stored gas and the total system mass. To use more than one container, when large amounts of gas are needed for a given application, is therefore quite normal. The tanks are then connected, typically in parallel, to a common pressure regulator, followed by a buffer tank for the working pressure of the fluid.
In the published US patent application US2003/0226365 A1, a hydrogen storage and supply system is disclosed. Cold containers, typically of spherical shape, stores hydrogen in porous material and hydrogen is retrieved by letting the gas exiting a port of the cold container. If several containers are used together, they are connected by a network of gas conduits.
In the published US patent application US2002/0046567 A1, hydrogen is also stored in cold containers inside one or several outer shells. Several containers may also be placed inside a common shell and are connected to each other either in a parallel or serial manner.
In the publication document DE 101 60 701 A1, gas containers arranged inside each other are disclosed. The inner and outer containers have typically different outlets. If more than one inner container is provided, the inner containers are connected in series and/or parallel to share one common outlet, however, different from the outer container outlet.
Systems of connected gas containers according to prior art become in many cases bulky and complicated. Furthermore, upon changing empty containers for filled ones, the connections to the empty containers have to be dismounted and connections to the filled ones have to be arranged for. Such procedures are time consuming and may also be hazardous if performed by non-skilled persons. Situations where gas containers are to be used in consumer products thus require additional safety arrangements.